Sizing is a metal finishing process that can be used for finishing a forged article requiring good dimensional accuracy, such as a gear and the like. The sizing is generally performed within a closed die, as shown, for example, in Japanese Patent Application Laid-open Publication (JP-A) No. 09-010883.
In the sizing process shown in JP 09-010883A, a helical gear member as a primary forged article is constrained on its circumference by a helical gear die having internal sizing helical gear teeth and held in a floating state, and while keeping this condition, the helical gear member is press-formed from above and below by upper and lower punches each having helical gear teeth same as those of a finished helical gear and axially movably engageable with the internal sizing helical gear teeth of the helical gear die. The helical gear member as the primary forged article can thus be sized into a helical gear having sized gear teeth of desired dimensional accuracy.
Quality of the sizing gives a great influence upon the service life of gears. In view of an increased demand for a long-life, high-accuracy gear or the like mechanical component, it is highly desirable to provide a sizing technique which is capable of finishing gear teeth to ensure better dimensional accuracy and surface finish.
It is accordingly an object of the present invention to provide a sizing method and a sizing apparatus which are capable of finishing a roughly forged part of a mechanical component with better dimensional accuracy and surface finish.